1. Field of the Invention
The present invention generally relates to the method and the ion implanter of real time monitoring ion beam, and more particularly, is focused on real-time monitoring the ion beam when the Faraday cup is at least partially blocked.
2. Description of Related Art
Ion implantation is widely used in the semiconductor manufacture, for example, to implant wafers with desired. ions of desired energy. Ion implantation usually requires a uniform distribution and consistent amount of ions beam to be implanted into a wafer.
FIG. 1 is a diagram for a conventional ion implanter 100. The conventional ion implanter 100 could implant specific ions with desired energy on a wafer 20. The ion implanter 100 has an ion source 110 capable of generating an ion beam 10. The ion beam 10 generated from the ion source 110 is analyzed by an analyzer magnet 120 and travels along a desired trajectory. The analyzer magnet 120 includes a beam exist 121, a beam entrance 122 and a magnet field. space 123. Herein, as well-known knowledge, the magnet filed in the magnet field space 123 is adjustable. Hence, ions with undesired mass and/or undesired energy strike on the shell of the analyzer magnet 120, and then are removed from the ion beam 10. After that, the ion beam 10 passes through the beam exist 121 and could be projected on the wafer holder by the wafer holder 20. The conventional ion implanter 100 further includes one or more acceleration/deceleration electrodes 131, one or more magnets 132 and plasma flow gun 133. The acceleration/deceleration electrodes 131 apply at least one electric field on the ion beam 10 so that the energy of the ion beam 10 is adjusted, and the magnets 132 separately apply at least one magnetic field on the ion beam 10 so that the shape of the ion beam 10 is adjusted. The plasma flow gun 133 emits plasma or electrons crossing the ion beam causing the ions have electric neutrality since the ions are positive chargers. In addition, FIG. 1 is only a schematic diagram, which does not show the real variations of the beam shape, beam size, beam path and so on, which also does not show all potential elements inside the ion implanter 100.
As mentioned above, the conventional ion implanter measures and receives the ion beam by the Faraday cup 127 positioned downstream the wafer 20. Since the wafer holder 20 moves relatively to the ion beam such that the ion beam can implants into the whole wafer 20, during some portions of the process, the Faraday cup 127 may be at least partially blocked by the wafer holder 20 (or by the held wafer or other relative hardware) and can not receive and measure the ion beam.
If the current of the ion beam or the operation of the ion implanter is stable, the problem mentioned above no longer exists or could be ignored. However, when the current of the ion beam or the operation of the ion. implanter is unstable, then the variation of the implantation of the wafer 20 resulting from the relative movement between the wafer and the ion beam can not be ignored. In other words, if the ion beam path occurs a deflection, which can not be monitored before or during the ion implantation process. Therefore, the difference between the real implantation and the predetermined implantation can not be monitored effectively.
Particularly, when the precision requirement of the ion implanter is higher or the scale of devices formed on the wafer becomes smaller, for example the newly present device with a critical dimension about 22˜28 nm, the problem mentioned above will be more serious.
For the disadvantage mentioned above, there is a need to propose a novel and useful approach for monitoring the real-time condition of the ion beam during the ion implantation process.